The chemical control of respiration in patients with chronic obstructive pulmonary disease receiving various concentrations of inspired oxygen will be studied. In particular, the relationship of blood ammonia, and cerebrospinal fluid ammonia and amino acid concentrations to depression of ventilation during oxygen therapy will be emphasized. Basic studies of the respiratory control system will be carried out in experimental animals, in order to develop an accurate dynamic model of the system. The influence of feedback from stretch receptors in the lung on the respiratory responses to step forcing of the carotid chemoreceptors with either hypercapnic or hypoxic blood will be determined.